This invention relates to a technique for the manufacture of a semiconductor integrated circuit device, particularly to a technique effective when applied to the manufacture of a semiconductor integrated circuit device having a MISFET equipped with a metal gate electrode.
Japanese Patent Application Laid-Open No. SHO 59(1984)-132136 (Kobayashi, et al., corresponding to U.S. Pat. No. 4,505,028) discloses a technique wherein a gate electrode having a metal structure is formed from a W film (or Mo film) on a Si (silicon) substrate and then, the resulting electrode is oxidized in a mixed atmosphere of water vapor and hydrogen, whereby only Si is selectively oxidized without oxidizing the W (Mo) film. This technique makes use of the fact that a water vapor/hydrogen partial pressure ratio at which the redox reaction is in equilibrium is different between W (Mo) and Si. Selective oxidation of Si is carried out by setting this partial pressure ratio within a range which provides for the reduction of W (Mo), but the oxidation of Si.
Japanese Patent Application Laid-Open No. HEI 7(1995)94716 (Muraoka, et al.) discloses a technique wherein a gate electrode of a polymetal structure including a metal nitride layer such as TiN and a metal layer such as W is formed over an Si substrate via a gate oxidized film and then, the resulting substrate is oxidized in a reducing gas (hydrogen)+oxidizing gas (vapor vapor) atmosphere diluted with nitrogen. According to this technique, only Si can be selectively oxidized without oxidation of the metal layer and at the same time, oxidation of the metal nitride layer can be prevented, because identification from the metal nitride layer can be prevented by diluting the water vapor+hydrogen gas mixture with nitrogen.
Japanese Patent Application Laid-open No. SHO 60(1985)-160667 (Agatsuma) discloses a technique wherein a thin film made of a refractory metal such as W or Mo is formed over a silicon substrate and then, the resulting substrate is heat treated in a non-oxidizing atmosphere to diffuse oxygen occluded in the thin film to the surface of the substrate, whereby an extremely thin silicon oxide film is formed on the interface between them.